1. Field of the Invention
The present invention generally relates to electronic assemblies surrounded by enclosures that prevent passage of electromagnetic or radio frequency interference (RFI). Enclosing structures combine shield members with ground planes associated with the electronic assemblies. The present invention relates to structures for electrically connecting shield members to ground planes.
2. Description of the Related Art
Electronic assemblies, containing interference sensitive or signal generating devices, require isolation by shield members and ground planes to protect the devices or prevent damage by the signals they emit. Shield members must act as a shield for electromagnetic and radio frequency waves. The interference caused by such waves in electronic devices is commonly referred to as electromagnetic interference (EMI) or radio frequency interference (RFI), hereinafter jointly referred to as EMI.
Effective EMI shielding requires electrical continuity between an EMI shield and a ground plane associated with, e.g. a printed circuit. A suitable form of EMI shield comprises an enclosure surrounding an electronic assembly. The enclosure often has several parts suitably connected to form an electro-conductive structure around the assembly. Required parts include a ground plane associated with the electronic assembly and an EMI shield member, electrically connected to the ground plane.
JP-B2 7-63114 describes an EMI shielding structure wherein an EMI shield member has a shield plate fixed to its inner surface. After placing the EMI shield member in desired alignment over an electronic assembly, application of pressure brings the shield plate into resilient contact with a ground plane of a printed circuit.
JP-A 9-138389 describes an EMI shielding structure using a frame ground consisting of two metal strips. The frame ground is soldered to an EMI shield member and also to a ground plane of a printed circuit.
JP-A 10-62756 describes an EMI shielding structure wherein an EMI shield member, which has been pressed out to form protuberances, is used, and the protuberances are brought into contact with a ground plane of a printed circuit.
JP-A 7-248481 describes an EMI shielding structure wherein an EMI shield member is formed with a ground terminal, and the ground terminal is fitted into a connector terminal on a ground plane of a printed circuit.
JP-A 7-333638 describes an EMI shielding structure wherein an EMI shielding film covers a printed circuit. The EMI shielding film consists of a conductive layer, an insulating layer, and an adhesive layer. With the adhesive layer, the EMI shielding film is adhered to the printed circuit.
Referring to FIG. 11, an EMI shielding structure according to a less preferred embodiment will be described. A printed circuit 110 supports electronic components, not shown, that are protected by an EMI shield member 112. A plurality of conic contact protuberances, only one shown at 111, are formed on the printed circuit 110. Each contact protuberance is part of the ground plane of the printed circuit 110. After placing the EMI shield member 112 in desired alignment over the electronic assembly, application of pressure brings the inner surface of the EMI shield member 112 into contact with the vertex of each contact protuberance 111. Electrical connection between the EMI shield member 112 and the contact protuberances 111 may be ensured by joining them by solder.
Modules are now widely used as electronic assemblies. Such modules are required to grow thinner and thinner to increase their competitive powers in market. A reduction in thickness of a module inevitably requires a reduction in thickness of at least some of its parts. The reduction in thickness of modules causes a drop in stiffness of the final product, such as a liquid crystal display (LCD), against bending stress.
If the EMI shielding structure is installed in such a LCD, application of pressure to the surface of the LCD may cause loose contact between some of the conical contact protuberances 111 and the EMI shield member 112. Occurrence of such loose contact may cause abnormality in image produced by the LCD.
According to the EMI shielding structure shown in FIG. 11, the vertex of each conical contact protuberance 111 and the EMI shield member 112 makes a point contact. Thus, an increased number of contact protuberances 111 are required to provide a sufficiently low resistance of the electrical connection between the EMI shield member 112 and the ground plane of the printed circuit 110.
In the EMI shielding structure shown in FIG. 11, the thickness, as indicated at B, of the EMI shield member 112 adds to an elevation of the remote surface of the EMI shield member 112 from the printed circuit 110. If each contact protuberance 111 has the height A, the final elevation of the remote surface of the EMI shield member 112 can be expressed as the sum (A+B).
As mentioned before, after placing the EMI shield member 112 in a desired alignment over the electronic assembly, application of pressure to the EMI shield member 112 causes contact between the vertexes of each contact protuberance 111 and the surface of the EMI shield member 112. However, it is difficult to confirm whether the contact protuberances 111 have been brought into contact with the surface of the EMI shield member 112.
The EMI shielding structure shown in FIG. 11 is satisfactory to some extent. However, a need remains for an EMI shielding structure, which is free from the above-mentioned shortcomings inherent with the EMI shielding structure shown in FIG. 11.